Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on a print medium in a particular order to form alphanumeric characters, area-fills, and other patterns thereon. Low cost and high quality of the hardcopy output, combined with relatively noise-free operation, have made ink-jet printers a popular alternative to other types of printers used with computers. Notwithstanding their recent success, intensive research and development efforts continue toward improving ink-jet print quality. A surge in interest in ink-jet printing especially in the area of photographic printing has resulted in the need to produce high quality prints at a reasonable cost. The challenge remains to further improve the print quality of ink-jet prints. The emerging use of ink-jet prints for digital photos, requires high-resolution images that have accurate color, are durable, and do not show banding of colors. By this invention, it has been found that the addition of black increases the detail in the dark areas of images; therefore, for best results a black ink is needed.
For text quality on plain paper, pigmented blacks are preferred because dye based inks have a tendency to wick along the paper fibers which reduces the sharpness of the edges However, pigmented blacks and dye-based colors do not combine for good image quality on photo media. Improving edge sharpness/text quality of dye based black inks would enable one black for both plain paper text and imaging on photo media.
This invention also concerns a method to improve the edge sharpness of dye based black inks on plain paper using cationic surfactants.
Color ink-jet printers, such as a DesignJet® printer available from Hewlett-Packard Company, typically use three inks of differing hues: magenta, yellow, and cyan, and optionally black. The particular set of colorants, e.g., dyes, used to make the inks is called a “primary dye set.” A spectrum of colors, e.g., secondary colors, can be generated using different combinations of the primary dye set.
In general, a successful ink set for color ink-jet printing must be compatible with the ink-jet pen and the printing system. Some of the required properties for the ink-jet ink include: good stability of the ink solution, the proper viscosity, the proper surface tension, no deleterious reaction with the printhead components, high solubility of the dyes in the vehicle, consumer safety and high color saturation. Another highly desirable performance of the inks is text with sharply defined characters, with minimal wicking, on photo as well as plain paper.
Inks are known which possess one or more of the foregoing properties. However, few inks are known that possess all the foregoing properties, since an improvement in one property often results in the degradation of another property. Thus, many inks used commercially represent a compromise in an attempt to achieve an ink evidencing at least an adequate response in each of the foregoing considerations. For example, inks are known which can obtain the color gamut comparable to silver halide prints, but, without software manipulation, cannot obtain the sharp, smooth edge appearance needed for crisp, un-blurred text printing. Accordingly, investigations continue into developing ink formulations which have improved properties and which do not improve one property at the expense of the others. Thus, there remains a need in the art to further improve the print quality and stability properties of the ink-jet prints without sacrificing pen performance and reliability and wherein the complexity of printer and software design is reduced.